Implantable electronic devices (IEDs) include implantable cardiac monitoring (ICM) devices (or loop recorders) used to monitor electrical activity of a heart and implantable pulse generators (IPGs), such as pacemakers, leadless pacemakers, and implantable cardioverter defibrillators (ICDs) used in the treatment of cardiac conditions, and neuromodulators or neurostimulators used in chronic pain management or the actuation and control of other body systems.
IEDs have traditionally used hard metal cases, lids, and glass to metal seal (GTMS) feedthrus to contain a battery stack. The cases are connected to the internal chemical potential either directly when the anode is attached to the case, or indirectly if the electrolyte contacts the case. The closed assembly is then placed inside another metal can that contains the rest of the electronic components. This case inside a can assembly method adds packaging inefficiencies from the metal case and can. In addition, the battery internal geometry is constrained to flat planes.
Moreover, this can inside a case approach of a conventional IED battery is often of a configuration that creates “dead space” within the implantable medical device (e.g., a can having a substantially square or rectangular shape). Although a thoughtful design approach can help to reduce the amount of such dead space, an appreciable volume of space within the IED typically remains unusable when employing a conventional IED battery. Also, the metal battery case that contains the active battery components must be of a thickness sufficient to protect against battery leakage. The thickness of the battery case must also be taken into consideration when allocating space within the IED to house a battery source of a conventional design.
It is well appreciated in the IED manufacturing industry that the battery component of an IED requires the allocation of an appreciable percentage of usable space within the IED and significantly impacts the physical configuration of the IED. It can, therefore, be appreciated that reducing the size of the battery is a desirable design objective. However, reducing IED battery size results in a corresponding reduction in battery capacity. A reduction in capacity limits the duration of service time within the patient before battery replacement is required. Battery replacement in many cases requires surgical replacement of the entire device. Thus, there are limits on the ability to make significant battery size reductions using conventional IED battery design principles.
An ICM device may record cardiac activity of a patient over time and report such cardiac activity to an external device. The ICM device may optionally perform various levels of sophisticated analysis of the cardiac activity and based thereon perform additional recording operations. In general, an ICM include a battery, memory and electronic circuitry that are hermetically sealed within a metal housing (generally referred to as the “can”). The metal housing typically is formed of titanium and includes a shell (e.g., opposed concave half shells that are welded together, a “deep drawn shell, etc.) to form a device housing with an interconnect cavity, in which the battery, memory, pulse generator and/or processor module reside. The half shells have an oval contour with a header receptacle area configured to receive a header assembly. A feed-through assembly is located at the header receptacle area and is sealed to the device housing to form an interface for conductors to enter/exit the interconnect cavity.
Most medical devices use sensor terminals isolated in leads or polymer headers to detect bio-electric signals. However, in an ICM, the device housing (“can”) may be used as a biosense electrode, and the same device can is used as the battery case, which is in contact with the electrochemical potentials of the battery. Because of this contact between the battery and the case, the housing becomes negative, i.e., case negative. In this way, the electrochemical potentials of the battery may introduce noise, negatively affecting biosensing of the ICM.
There is a need in the implantable electronic device manufacturing community for an IED battery implementation which provides for an overall flexibility in IED battery size, shape and form factor, without a corresponding reduction in battery capacity, and without imposing safety concerns that would render the medical device unsuitable for use. There is further a need for an ICM with an improved signal-to-noise ratio. The present invention fulfills these and other needs.